In the field of the electronic toll collection system (ETC) (registered trademark) (also referred to as “automatic toll collection system”), wireless communication is required to be correctly performed through radio waves with a plurality of vehicles which travel on lanes (travel lanes). However, there is concern about the occurrence of a malfunction caused by accidental wireless communication with an unexpected vehicle (e.g., a vehicle traveling on a neighboring lane, and the like) due to the influence of reflection of radio waves from road surfaces and buildings, and the like.
As a countermeasure against the above, a method of determining whether wireless communication with an intended vehicle is being correctly performed by obtaining an angle of arrival of radio waves transmitted from an on-board unit mounted in a vehicle and measuring the spatial position of the vehicle (on-board unit) is being examined (refer to Patent Literature 1, for example).
Meanwhile, as a means for obtaining an angle of arrival of radio waves, for example, a method of receiving radio waves from an on-board unit using a dedicated array antenna (also called an angle of arrival (AOA) antenna) having a plurality of antenna elements arranged in parallel and detecting the angle of arrival on the basis of phase differences between signals received by the plurality of antenna elements may be conceived.